1. Field of the Invention
The present invention relates to a heating system for a vehicle including a viscous fluid heater. More particularly, the present invention relates to a vehicle heating system including the viscous fluid heater where the rotor rotates to shear the viscous fluid for generating heat, and the generated heat is transferred to circulating fluid.
2. Description of the Related Art
Much attention has recently been focused on engine-driven viscous fluid heaters as auxiliary heat sources for vehicles. For example, Japanese Unexamined Patent Publication No. 2-246823 discloses a vehicle heating system incorporating a viscous fluid heater. The heating system includes a heating circuit having an engine-driven pump and a heater core (heat exchanger) used for warming the passenger compartment. The pump circulates engine coolant water between a water jacket of the engine and the heater core. Specifically, the engine coolant water is discharged from the outlet of the pump and passes through the heater core. The water is then drawn back to the inlet of the pump. A viscous fluid heater is located between the heater core and the engine water jacket. The heater is activated when the temperature of the coolant in the circuit is equal to or lower than a predetermined temperature.
Since the viscous fluid heater is used as an auxiliary heat source and is incorporated in the heating circuit, coolant water discharged from the viscous fluid heater is used for cooling the engine and is then drawn into the heater. The water is heated by heat exchange in a heat exchange chamber of the heater and is discharged to the heating circuit. However, one pass through the heat exchange chamber does not heat the water to a sufficient temperature for heating the passenger compartment, but slightly raises the water temperature (a few degrees at a time). Therefore, the water needs to pass through the heat exchange chamber several times until its temperature reaches the sufficient temperature. Also, recent progress in automobile technology has improved the efficiency of the engine. Therefore, current engines produce less heat than before. This reduces the amount of engine heat that is used for heating coolant water.
In the above described heating system, the heat added to the coolant water by the viscous fluid heater is used for warming the engine when the engine is not warmed. This slows the warming of the passenger compartment.